1. Field of the Invention
This invention relates in general to multi-wall bag constructions. More particularly, the invention relates to the adhesive lamination of multiple plies of sheet material to form a multi-wall structure which may be folded to define a bag, and which, in a preferred embodiment, defines a bag for receiving, storing and popping a quantity of popcorn kernels in a microwave oven.
2. Background of the Invention
There are many known containers for storing and cooking food, including microwavable bags for popping popcorn. Such bags are typically formed of multiple plies of paper adhesively laminated together to form a multi-wall construction, and have a microwave susceptor in one panel for absorbing microwave energy and heating the contents of the bag. In conventional constructions, the entire confronting area between the plies is coated with adhesive, whereby the adhesive forms an essentially continuous layer between the plies of paper. This construction uses a large amount of adhesive and results in a relatively stiff wall, which degrades the performance of the bag and increases its cost. For instance, the expanded shape of the bag is affected by the stiffness of the wall, and may not be aesthetically pleasing or optimal for full cooking of the food contained in the bag.
Some prior art bags have been constructed with the plies or laminations forming the wall of the bag secured together with spaced, discrete areas or patches of adhesive, rather than coating the entire confronting surface between the plies with adhesive. However, the utilization of spaced patches of adhesive in these prior art constructions is for the purpose of producing an insulating wall structure, or forming an expandable shape that causes the inflating bag to move or shift its position in the heating chamber as the bag expands during cooking, or to enable one ply to move relative to the other. Examples of such prior art constructions are shown U.S. Pat. Nos. 1,953,686, 3,098,563, 5,081,330 and 5,317,118.
U.S. Pat. No. 1,953,686 to Natwick describes a bag for use in forming bricks of carbon black, and secures the plies "a" and "b" of the bag wall together with spaced patches of adhesive "c", so that the plies can shift relative to one another during compression of the bag and its contents. The spots of adhesive are intended merely to tack the plies together, rather than to form a unitary laminated wall structure, and cover probably less than ten percent of the confronting area between the plies. The wall of this bag thus comprises two separate walls that are merely held in juxtaposition to one another by the spots of adhesive, rather than to form a unitary laminated structure.
U.S. Pat. No. 3,098,563 to Skees describes an inflatable heat insulating structure in which an expandable fluid is placed between the plies of the wall, and the inner and outer plies are sealed together around their periphery to prevent escape of the fluid, and at spaced points across their area to prevent excessive bulging or rounding of the structure as the fluid between the plies expands to expand the plies apart in their unsecured areas to form expanded insulation chambers.
U.S. Pat. Nos. 5,081,330 and 5,317,118 both describe structures in which adhesive is applied between the plies in spaced patches to define a plurality of discrete sealed chambers or pockets which expand when the bag is heated to define insulation chambers.
None of the prior art suggests a bag whose wall is formed of multiple plies secured together by spaced patches of adhesive to form a unitary laminated wall structure which uses less adhesive and which has greater flexibility than conventional bag wall structures, and which, due to its greater flexibility, has at least equal or improved performance and aesthetics as compared with conventional bags.
Consequently, a need exists for an inexpensive and effective way of constructing a multi-wall bag formed of multiple plies of paper secured together by spaced patches of adhesive to define a unitary structure which requires less adhesive than conventional bags, thereby costing less, and which also has greater flexibility for improved performance and aesthetics.